1. Field of the Invention
This invention relates generally to valves and more particularly to check valve assemblies which allow fluid to flow only in one direction within a conduit.
2. Description of the Prior Art
Houses and other structures are provided with chimneys, flues and other exhaust conduits to allow fumes from furnaces, stoves and the like to escape into the ambient environment. As one example, most stoves have a hood suspended above their burners for collecting cooking fumes and smoke, and an exhaust conduit which extends from the hood to the outside of the home. When the burners are being used heated air, smoke and particulate matter are drawn up the conduit, usually with the aid of an electrically powered fan, and safely vented outside.
A problem occurs when the burners are not being used and the fan is turned off. In this situation, cool air can rush down the conduit and into the home environment and warm air can slowly leak out. Thus a great deal of energy is wasted trying to maintain a house at a constant temperature due to a continuous influx of cool air from outside the house. This energy wastage could be eliminated by providing the venting conduit with a check valve which would allow exhaust fumes to escape but which would prevent cool air from flowing down the conduit from the outside.
The prior art is rich with examples of check valves used for similar applications. Most of the prior art check valves are of the "butterfly" type and are provided with some means for biasing the valve towards its closed position. Three examples of prior art check valve assemblies are described in U.S. Pat. Nos. 3,941,151 of J. Biddle; 1,301,455 of O. Kiessig; and 859,139 of I. Spencer. Each of the described assemblies includes a butterfly type valve disposed within a cylindrical sleeve which can be attached over or within an end of a conduit or pipe. A disadvantage with this type of assembly is that, for it to be used, an end of a conduit or pipe has to be easily accessible and free of obstructions.
Other types of check valve assemblies, such as the one described in U.S. Pat. No. 1,743,731 of W. Scott are designed to be disposed within a continuous length of conduit. Usually, however, such devices are ill adapted to be retrofitted into existing conduits and thus are mostly limited to new installations.
A problem that the prior art apparently has not addressed is how to safely and easily retrofit a check valve assembly within an existing conduit structure without modifying the structure in any way. All known prior art assemblies that are retrofittable within a conduit need to be anchored therein by forming one or more holes through the walls of the conduit and extending an anchoring pin therethrough. While U.S. Pat. No. 4,039,004 or R. Luthy describes the use of a resilient elastomer for attaching a backflow valve to a pipe fitting, Luthy's device cannot be retrofited within a conduit proper.
Another problem not solved in the prior art is how to construct a universal check valve assembly which can be adjusted to fit within differently sized conduits. All known prior art check valves have a fixed diameter and thus can only be used with a conduit having that same diameter.
The following U.S. Pat. Nos. are felt to be related to the present invention, although in no way anticipatory thereof: 3,951,051; 3,589,268; 3,584,566; 3,311,302; 3,285,155; 3,187,768; 2,825,275; 2,568,355; 2,599,075; 1,628,644; 1,503,915; and 756,046.